Specific difference in root penetration into the compacted soil cakes in crop plants

Artificially compacted soil cakes were used to examine the penetration of seminal roots in cereal and tap roots in leguminous crops. Using an oil pressure pump, compacted soil cakes 1 cm in thickness were made from sandy loam soil which had been sieved through a 2.54-mm screen and had about 13% moisture by volume. The penetration of seminal and tap roots of 30 common and forage crops was examined at 25°C. All crops except maize (Zea mays L.) could penetrate soil cakes with a hardness of more than 11 kg cm^-3. Among the crops used, the seminal root of six-row barley (Hordeum vulgare L.) could penetrate the hardest soil cake (73 kg cm^-3). Of the leguminous crops, the tap root of moth bean (Phaseolus aconitifolius Jacq.) could penetrate a soil cake of 59 kg cm^-3. The seminal roots of 7 crops and tap roots of 4 crops penetrated completely through soil cakes of 11 kg cm^-3. Among cereal crops except maize, there is a tendency of the larger the diameter of the seminal root, the stronger the penetration force. On the contrary, among leguminous crops except white clover (Trifolium repens L.), the smaller the diameter of the main root, the stronger the penetration force.